bug#73592: 30.0.91; delayed output with completion preview mode

[Eli Zaretskii <eliz@gnu.org>]

> From: Christopher Howard <christopher@librehacker.com>
> Date: Tue, 01 Oct 2024 15:04:57 -0800
> 
> 
> Hi, I don't know if I've done enough troubleshooting yet to justify opening this bug, but I been struggling with this since I switched to emacs-30 branch, and was wondering if others have experienced this also. I have not been able to reproduce the problem with -q so I suppose it must be an issue in my configuration or modes that I use.
> 
> I use global-completion-preview-mode with Completion Preview Exact Match Only set to on and Completion Preview Idle Delay set to No delay. When I am in eshell, or running eshell-command, I sometimes see this behavior where character output is either delayed briefly (like, one second), or a character is not outputted until I press another character, at which point both are outputted at the same time.
> 
> A reproducible case (for me at least) is if I am in eshell and I type the command "gnus". It takes about a second extra for the "s" to appear.
> 
> If I turn CP mode of the behavior goes away. I've been experimenting with leaving CP mode on and turning off my other minor modes, like Helm, but this hasn't had any effect so far.
> 
> I haven't had time yet to bisect my init.el — a rather long and tedious process in my case. Wondered if anybody might have some ideas as far as the likely culprit for this behavior.

Thank you for your report.

One way to find the possible culprit(s) is to run the commands with
slow responses after enabling the Lisp profiler (M-x profiler-start),
and then looking at (and possibly posting here) the produced profile,
after fully expanding it.

Eshel, can you please look into this?